This invention relates to a mechanically bonded composite article and to a process for its manufacture. A primary application of the invention is in the field of seals and gaskets.
Many plastics are often difficult to bond to one another or to elastomers. For example, articles of fused polytetrafluoroethylene (herein referred to as TFE) are not easily bonded to elastomers or to other materials. Yet, due to its low coefficient of friction and chemical inertness, this material provides advantages in the art of seals, gaskets, bearings and other environments. However, the application of TFE to this environment has been complicated by its high thermal coefficient of expansion, its lack of easticity and the difficulty of bonding it to other materials.
To overcome such complications, the prior art suggests the addition of an elastomeric layer to the fused TFE article. Thus, a composite TFE elastomer seal would provide the desired low friction and inertness of TFE, while the elastomer would provide elasticity and resilience. Prior art attempts to bond these materials have not been completely satisfactory. Adhesive bonding materials such as Hylene M-50 sold by E. I. duPont de Nemours & Co. has been suggested. Similarly, mechanical bonds have been used. These mechanical bonds have included the formation of interstices in one of the materials which are filled by the other material to achieve a mechanical interlock. These interstices may be formed by etching a sintered TFE article or by incorporating in the TFE powder a material such as methyl methacrylate which, upon sintering, vaporizes and leaves voids in the sintered article.